Katie’s done another video! This time it’s a neat method for constructing an egg-shape, using arcs of circles.

Bonus challenge: See if you can count how many times Katie accidentally says ‘compass’ instead of ‘pair of compasses’ during the video.

Katie’s done another video! This time it’s a neat method for constructing an egg-shape, using arcs of circles.

Bonus challenge: See if you can count how many times Katie accidentally says ‘compass’ instead of ‘pair of compasses’ during the video.

I’ve done another maths video! If you missed it earlier this week, here’s a nice mathematical card trick I learned recently on a trip to Finland. Enjoy!

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I was invited to give a talk for Ustinov College’s Café Scientifique on π Day this year. The turnout wasn’t great and I put quite a bit of effort into the slides, so I wanted to put it online. I’ve finally got hold of the recording, so here it is. Unfortunately they didn’t set the camera’s exposure properly, making the screen illegible, so you’ll probably want to follow along with the slides in another window.

*I tried to come up with a way of writing today’s date as a multiple of π Day, but couldn’t make it work. However, I did realise that Halloween (31/10) is the best approximation to π between now and the next π day (I think). Sπooky!*

I rediscovered this nice paper by Kenneth P. Bogart in my Interesting Esoterica collection, and decided to read through it. It turned out that, while the solution presented is very neat, there’s quite a bit of hard work to do to along the way. I’m not particularly experienced with combinatorics, so the little facts that the paper skips over took me quite a while to verify.

Once I was happy with the proof, I decided to record a video explaining how it works. Here it is:

*I probably made mistakes. If you spot one, please write a polite correction in the comments.*

My maths object this time is one of my dog’s favourite toys: the Nobbly Wobbly.

In the video, I said it was invented by a mathematician, but Dick Esterle’s bio normally goes “artist, architect, inventor”. I’ll leave it up to you to decide if Everyone’s a Mathematician.

It’s a particularly pleasing rubbery ball thing made of six interwoven loops in different colours, invented by Dick Esterle.

On Google+, various people told me the unexpected fact that the outer automorphism group of $S_6$ is hiding inside this dog toy.

I’ve also found this Celebration of Mind livestream starring Dick Esterle from 2013 talking about all sorts of mathematically-shaped toys, including the Nobbly Wobbly.

I’ve just posted my latest YouTube video, in which I explain how to use binary numbers to jazz up your nail varnish:

Alongside this video, I also have an associated puzzle for you to think about.

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Reader Marc Chamberlain sent this video in a bit too late to get in our advent calendar, but it’s about the 12 days of Christmas so we’re still cool, right?